In-Depth Notes on Cell Structure and Microscopy

A2.2 Cell Structure

Features Common to All Cells

• Basic Unit of Life: All living organisms are composed of cells, which are considered the basic structural and functional units of life.
• Common Features:
  • Plasma Membrane: Encloses cell contents and regulates substance entry and exit.
  • Cytoplasm: Contains water, enzymes, and other substances for metabolic reactions.
  • DNA: Contains genetic information for cell function and protein synthesis.

Diversity of Cell Structure

• Differences Between Cells: While cells share common features, there are significant variations among different types of cells.
• Eukaryotic vs. Prokaryotic: Eukaryotic cells have a defined nucleus, while prokaryotic cells lack a nucleus and consist of a nucleoid region.

Cell Theory

• Origin: Formulated in the 17th century, with contributions from Robert Hooke.
• Implications: Suggests that all living organisms consist of one or more cells.
• Limitations: Certain structures, like viruses, do not conform to traditional cell theory.

Microscopy and Cell Investigation

• Microscopy Power: The human eye can resolve down to about 0.1 mm, while microscope resolving powers can reach nanometer ranges (e.g., electron microscopes can resolve down to 0.1 nm).
• Types of Microscopes:
  • Light Microscopes: Use light and lenses to magnify samples.
  • Electron Microscopes (EM): Use electron beams for much higher resolution; types include
  • Scanning Electron Microscope (SEM): Provides 3D images of surfaces.
  • Transmission Electron Microscope (TEM): Used for viewing internal structures but requires thin sections.

Microscopy Skills

• Making Preparations: Techniques for preparing slides, including making temporary mounts and using stains for better contrast.
• Calibration: Understanding the use of eyepiece graticules for measuring sizes within samples.

Structures in Cells

• Common Eukaryotic Structures:
  • Nucleus: Double membrane containing DNA wrapped around histone proteins.
  • Mitochondria: Sites of aerobic respiration, producing ATP.
  • Chloroplasts (in plants): Responsible for photosynthesis; contain chlorophyll.
• Differences in Eukaryotic Cells:
  • Animal Cells: No cell wall, smaller vacuoles, but centrioles are present.
  • Plant Cells: Have a thick cell wall made of cellulose, large central vacuoles, and plastids.
  • Fungal Cells: Contain chitin in cell walls and may have varying structures (e.g., septate vs. aseptate hyphae).

Processes of Life in Unicellular Organisms

• Vital Functions:
  • Metabolism: Includes all chemical reactions necessary for life.
  • Nutrient Uptake: Organisms must acquire nutrients for energy and growth.
  • Waste Excretion: Removal of metabolic waste to maintain homeostasis.
  • Reproduction: Can occur asexually or sexually.

Atypical Cell Structures

• Examples of atypical structures include:
  • Red Blood Cells: Lack a nucleus and have a biconcave shape for flexibility.
  • Phloem Sieve Tube Elements: Modified structures for nutrient transport in plants.
  • Skeletal Muscle Fibers: Multinucleate structures resulting from cell fusion.

Conclusion

• While there are commonalities in cell structure, the diversity in cell types reflects the wide range of functions and adaptations in living organisms. The advancements in microscopy and understanding of cellular mechanisms continue to enhance our knowledge of biology.